1. Technical Field
The present invention relates to a method of manufacturing a semiconductor device usable as a sensor, such as an acceleration sensor and an angular velocity sensor, that comprises a movable section formed in a semiconductor layer of a semiconductor substrate and displaceable in response to a dynamic quantity acting thereon.
2. Related Art
A conventional semiconductor device of this type has been for example disposed by Japanese Patent Application Laid-open No. 11-274142. This semiconductor device uses an SOI substrate formed as a semiconductor substrate, in which the substrate is composed of a first silicon layer (a first semiconductor layer), an oxide layer (insulation layer) layered on the first silicon layer, and a second silicon layer (a second semiconductor layer) layered on the silicone oxide layer.
For manufacturing the above semiconductor device, a trench to demarcate a movable section is formed. Specifically, a first step of dry etching is performed so that the trench is formed to reach the oxide layer from the surface of the second silicone layer. Then a second step of dry etching is performed to apply etching ions to a partial region of the second silicon layer, which is located laterally to the bottom of the trench. This etching allows the partial region of the second silicone layer to be removed, thus providing a movable section formed by the remaining area of the second semiconductor layer.
The foregoing manufacturing step of the movable section will now be detailed. Through the second step of try etching, which is done after forming the trench, a partial region of the insulating film, which is located at the bottom of the trench, is charged at first. This charge causes etching ions to be repelled during the dry etching continued, so that etching ions travel as they change their courses from the depth direction of the trench to the lateral direction orthogonal thereto. Accordingly, the etching ions are forced to impinge onto a partial region of the second semiconductor layer, which is located on the sides of the bottom. The partial region of the second semiconductor layer is thus subjected to the etching so that it is removed, providing a movable section above the insulation layer.
In the case of the technique disclosed by the above conventional patent publication, an etched depth is detected by utilizing movable sections formed dedicatedly to detecting the etched depth. The foregoing charging is used to stick (bond) the adjacent depth-detecting movable sections to each other.
However, the estimation of the foregoing manufacturing technique carried out by the inventors showed two problems.
One problem is that a sticking phenomenon may arise among members of the semiconductor substrate. In addition to the insulation layer at the trench bottom, the dry etching carried out after forming the trench charges not only the movable section responsible for a sensing part of the device but also the second semiconductor layer and insulation layer which are located oppositely to the trench via the movable section. This charging brings about an imbalanced charging distribution among such various members, so that there is a fear that the members are partly or entirely subjected to sticking phenomena to their surrounding members.
The other problem also relates to the sticking phenomenon due to deposits. During the performance of the dry etching to remove regions of the second semiconductor layer, which are located on the sides of the trench bottom, deposits that appear due to the etching ions may adhere on a region of the movable section, which is opposed to the insulation layer. The deposits are composed of for example polymers including fluorine, carbon and oxygen.
If the deposits adhere on the movable section, as stated above, both the movable section and the insulation layer are likely to be stuck to each other at the locations of the deposits. One reason is that the deposits make it narrow the distance between the movable section and the insulation layer.
In cases where the movable section which should operate as the sensing part to the device fall into the stuck state on account of the foregoing charging or deposits, it is no longer possible to make the movable section operate normally as the sensing part of the device.